Task: Document Purchase delete and cancel API endpoints

### Details

Currently, the parameters for V1 API endpoints /me/purchases/:purchase_id/cancel and /me/purchases/:purchase_id/delete are not documented. While `delete` only requires a purchase_id, the cancellation endpoint requires multiple parameters, based on the product it has to cancel.

It's important to note the the V1 endpoints might be replaced by new V2 endpoints that also have documented with the same parameters.

### Checklist

_No response_

### Related

_No response_

Start by locating the documentation or endpoint definitions for /me/purchases/:purchase_id/cancel and /me/purchases/:purchase_id/delete. Confirm whether the V1 endpoints remain in scope or are superseded by V2, then identify the cancellation parameters for each product. Done means both endpoints document their required parameters, including purchase_id.

Written by the indexing model from the issue text.